This application is being concurrently filed with the following applications: "Process and Architecture for Digital Micromirror Printer," Ser. No. 08/038,398, TI-17632; and "Gray Scale Printing Using Spatial Light Modulator," Ser. No. 08/038,391, TI-17611.
1. Field of the invention
This invention relates to printing systems, more particularly with printing systems using spatial light modulator arrays.
2. Background of the invention
Printing systems trying to achieve gray scale can use spatial light modulators in several ways. The arrays usually have to be defined to a specific dimension, making each type of printing application require a different device. Desktop electrophotographic printing using highly sensitive media, at 600 dots-per-inch (dpi), needs one configuration of a device or devices, whereas a computer to plate offset system using relatively insensitive media needs another. This translates into high cost, low volume production runs. Yet, the needs of different systems must be met.
The computer to plate systems need large arrays that can time delay and integrate (TDI). The image data for one line on the board passes from line to line on the device, keeping the image data for that line on the board the entire time the board is under the device. This gives high energy transfer onto the photosensitive media, which does not have very high sensitivity. A typical array for this application may have as many as 256 rows. This appears satisfactory for printing, allowing 256 gray shades.
However, desktop printing has a different problem. Because of the curvature and movement of the drum, it is nearly impossible to optically "wrap" a 256-row device around it. Yet, 256 rows of gray scale gives printing system users what they need. Therefore, some way must be developed to allow a smaller device to achieve gray scale, and still make those same devices compatible with systems that have different needs.